The invention relates to the area of plug-in computer modules, particularly for application to laptop, notebook, or other portable computer products where small size, power conservation, and harsh environment such as shock, vibration, and temperature are important considerations.
Conventional computer packaging architectures typically employ a backplane, consisting of an array of identical multipin connectors wired in a parallel bus configuration to the power supply, address, data, status, and control signals from the host computer. Peripheral cards, or modules, such as IC memory, having mating multipin connectors, can be plugged-in to the backplane positions, and thus communicate with the host computer.
A number of problems arise as a result of this scheme, including:
Current 32-bit computers require a very large number of pins--for the backplane connector, typically 96 pins or more. The parallel bus method makes the connector expensive, power and board-area hungry, and design-difficult due to high-frequency cross talk, reflection, and termination problems of the backplane traces.
Large multi-pin connectors have serious environmental constraints and are particularly sensitive to shock, vibration, contamination, and wide ambient temperature exposure.
In applications where frequent module insertion and extraction is needed, as for example, IC memory cards, the high mating force resulting from the large pin count is an ergonomic drawback. The wear of the contacts is also a problem, and leads to eventual unreliability of the connection.
The number of pins on the connector determines the maximum address size, so that expansion of the design is limited. A 64-bit processor, for example, would require a 64-bit address and data scheme, and therefore twice as many pins as a 32-bit processor.
Since the host power supply is used by plug-in modules, there is no ohmic isolation of the circuitry. This can result in ground loops, noise, and other problems with modules used for analog functions. In the case of medical instrumentation, there is no inherent isolation of the patient from the circuitry.
The power supply voltages available to the module circuitry are those defined by the host. In VME bus systems, for example, +5 logic and .+-.12 volt supplies are used. Many new types of integrated circuits require still different voltages or other supply specifications such as very tight voltage regulation.
The logic levels for the backplane signals must be carefully specified and identical for all modules. Thus, TTL signal levels are different from CMOS signal levels, even when both circuits use the same +5 power supply. Furthermore, recently adopted 3 volt logic ICs cannot interface directly, nor can mixed 5 volt and 3 volt systems be implemented easily.
These problems and others can be minimized or eliminated by replacing the connector function with a design using non-contact technology. This general concept has been previously attempted for so-called "Smart Cards" used in financial and transaction-oriented markets. Various physical effects, including capacitive, inductive, hall effect, and optical coupling have been proposed for data and/or power transfer. To date, however, the technology has not allowed for efficient transfer of large amounts of power, nor the capability of very high data rates. Furthermore, "Smart Card" concepts generally use a major portion of the surface area of the card for the elements of the non-contact connection, and thus are not in a form suitable as a compact low-insertion force connector that is a separate element from the card or module. A separate or discrete non-contact connection scheme would offer universal application to many different module host designs. Examples of these prior efforts are found in U.S. Pat. Nos. 4,480,178; 4,605,844; 4,650,981; 4,692,604; 4,720,626; 4,791,285; 4,795,898; 4,797,541; 4,798,322; and 5,015,834.